The weakly bound complex NH3-CO: Observation and analysis of spectra in the infrared (C-O stretching) and millimetre wave (76-106 GHz) regions

The van der Waals complex NH3-CO has been studied in the infrared and milli metre wave regions, and analysed on the basis of the distinction between th e ortho- and para-NH3 nuclear spin species. The spectrum and energy level p attern of ortho-NH3-CO are relatively simple, closely resembling those of t he Ne-CO and Ar-CO complexes. The situation for para-NH3- CO is somewhat mo re complicated, with observed states having K values which differ by +/- 1 from that of the analogous ortho- NH3-CO state. This indicates that the low est energy orientation of para-NH3 in the complex lies in a II configuratio n. The present results correlate very well with the only previous study of NH3-CO, in the microwave region, and clarify the nature of the rotational s eries observed there. The infrared band centre of NH3-CO is only very sligh tly shifted (< 0. 2 cm(1)) from that of the free CO molecule, indicating th at the CO vibration has little effect on the intermolecular forces.